LAUSR

Non-orthogonal multiple access (NOMA) is becoming important in 5G, therefore, it is widely researched. Note that the users served in NOMA are often paired to prevent excessive interference. However, if the channel condition of direct downlink from the service node to one user is serious, the node may require the other user with better channel condition to relay this user’s signals, especially when the pure relay is difficult to deploy. This relay transmission is helpful for NOMA communication, but two problems should be considered: (i) how to persuade the relay user (i.e., the user with better channel condition) to expend extra resources for relay; (ii) how to suppress eavesdropping in the relay transmission, especially for the signals of indirect communication user (i.e., the user with worse channel condition). To solve these problems, we propose a novel signal-level scheme. In this scheme, on one hand, the node increases the spectral efficiency of relay user, and does the wireless power transfer to make the relay user supplement his/her energy by energy harvesting. On the other hand, a signal transformation method is designed to deal with each signal of indirect communication user. This transformation hides privacy information of indirect communication user, but does not disrupt the relay transmission. Utilizing the proposed scheme, the above problems are effectively solved by the compensation for the relay user and the signal protection for the indirect communication user.